Endless Stair, a towering structure of 15 Escher-like interlocking staircases made from American tulipwood CLT functioned both as a sculptural work and research project. Created originally for the 2013 London Design Festival, the structure pioneered the use of hardwood for cross-laminated timber, which is typically made from softwood, yet this project demonstrated the real potential for using tulipwood, an abundant, light and strong American hardwood.

Endless Stair is a publically accessible temporary sculpture designed to be endlessly reconfigured. A key objective for dRMM was to make the project environmentally friendly, with as little waste as possible in construction, and with the ability to re-use and relocate the modular design either in part, or as a whole.

Faced with the challenge from the London Design Festival to produce a sculptural, landmark installation, dRMM settled quickly on ideas involving stairs. Stairs are sculpture’s gift to architecture, where people experience space, pass each other and interact. This project served as vehicle for exploring structural and sculptural possibilities of tulipwood, donated by the American Hardwood Export Council, who were closely involved in the research and design process. The whole team worked in an incredibly collaborative way to overcome the challenges and complexities of the project within the time available.

Expert academic and product supplier advice was used to overcome particular gaps in knowledge. The University of Trento was central to understanding the essential rolling shear properties of the CLT, whilst the adhesive manufacturers helped specify the right type of glue to meet the manufacturing constraints and external use of the panels. One of the earliest decisions was to make the steps and the balustrades on one side from identical elements of CLT, equivalent in size. These are stacked up with a spacer element between them, creating the flights which, as a result of the stacking process, then step either to the right or to the left.

The interlocking stair design is a three-dimensional demonstration of in composition, structure and scale. Within this prefabricated construction, each piece is an essential part of the additive structure, indispensable within the load transfer path. Endless Stair is a fast and dry construction, easily demountable, and able to be entirely recycled on another site. This was recently demonstrated with a new, column-free composition, using seven of the original fifteen flights at the FuoriSalone 2014 exhibition in Milan.

The project was an opportunity to explore the properties of engineered hardwoods and understand the potential presented by the material. This spanned the full process of design, manufacture, construction and re-use at the structure’s ‘end of life’, and included investigations into material properties, the manufacturing process; design requirements for an accessible temporary art installation; and how Endless Stair could be built in front of the Tate Modern and one month later, de-constructed.

The wider aspiration remains that knowledge and experience gained from the series of reconfigurations of this engaging sculpture can inform the debate on higher performance timber structural design and the mainstreaming of hardwoods as an efficient engineered timber material.